Penetrable, epoxy resin composition comprising glycidyl ether of bisphenol modified with glycol or urethane, and inorganic filler

ABSTRACT

A penetrable, epoxy resin composition is disclosed which comprises: a liquid, epoxy resin mixture containing a glycidyl ether of bisphenol having an epoxy equivalent of 158-270 and a flexible epoxy resin which is a glycidyl ether of a bisphenol modified with a glycol or a urethane; a curing agent capable of reacting with the epoxy resin mixture when heated to a curing temperature; an inert organic solvent which does not react with the epoxy resin mixture, which is capable of dissolving the curing agent and which has a boiling point lower than the curing temperature; and an inorganic filler having an average particle size of 0.1-5 μm.

BACKGROUND OF THE INVENTION

This invention relates generally to an epoxy resin composition havingexcellent penetrability and, more specifically, to an epoxy resincomposition suitable for use in bonding a ferrite magnet to a motoryoke. The present invention is also concerned with a method ofpermanently fixing a ferrite magnet to a motor yoke.

One pack-type liquid epoxy resin containing a liquid epoxy resin blendedwith an inorganic filler together with a latent curing agent is knownand is used in various fields. In recent years, it has been proposed touse an adhesive for fixing a ferrite magnet to a motor yoke in lieu offixation by bolting. For this purpose, the use of such a one pack-typeliquid epoxy resin as mentioned above has been proposed. Knownadhesives, however, have poor penetrability so that it is difficult tocause the adhesive to penetrate, with satisfactory fluidity, into a fineclearance between the surfaces of the yoke and the ferrite magnet. Thus,with the use of the conventional adhesive, it is necessary to apply theadhesive onto the surface of the yoke and/or ferrite magnet beforeassembly.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide an epoxyresin composition excellent in penetrability into fine gaps betweenarticles to be bonded which are temporarily held together.

It is a special object of the present invention to provide a compositionof the above-mentioned type which is suited for bonding a ferrite magnetto a motor yoke.

It is a further object of the present invention to provide a method forbonding a ferrite magnet to a motor yoke with the above epoxy resincomposition.

In accomplishing the foregoing objects, there is provided in accordancewith the present invention a penetrable, epoxy resin compositioncomprising:

a liquid, epoxy resin mixture containing a glycidyl ether of a bisphenolhaving an epoxy equivalent of 158-270 and a flexible epoxy resin;

a curing agent capable of reacting with said epoxy resin mixture whenheated to a curing temperature;

an inert organic solvent which does not react with said epoxy resinmixture, which is capable of dissolving said curing agent and which hasa boiling point lower than said curing temperature; and

an inorganic filler having an average particle size of 0.1-5 μm, saidcomposition having a viscosity of 50-10,000 cP at 25° C.

In another aspect, the present invention provides a method of fixing aferrite magnet at a desired location on the surface of a motor yoke,comprising the steps of:

providing the above epoxy resin composition;

magnetically bonding the ferrite magnet to the motor yoke at the desiredlocation, at least one of the magnet and the yoke being so shaped that aclearance or gap of 0.02-1 mm is defined therebetween;

positioning the resulting assembly to maintain the gap in a vertical orslanted position;

applying a quantity of the epoxy resin composition on an upper portionof the gap; and

heating the assembly at the curing temperature, so that the epoxy resincomposition penetrates into the gap and is cured within the gap with thesimultaneous evaporation of the organic solvent.

Other objects, features and advantages of the present invention willbecome apparent from the detailed description of the invention tofollow.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, two types of epoxy resins are used incombination. One of them is a glycidyl ether of bisphenol having anepoxy equivalent of 158-270, preferably 175-270. By the term "epoxyequivalent" is meant "weight per epoxy" which is a weight (g) of theepoxy resin providing 1 g equivalent of the epoxy group. Illustrative ofsuitable glycidyl ethers of bisphenol are bisphenol A, bisphenol F andbisphenol AD epoxy resins. These glycidyl ethers may be used bythemselves or as a mixture of two or more.

The other type of the epoxy resin which is to be used in combinationwith the above glycidyl ether of bisphenol is a flexible resin,preferably one obtained by modifying the above glycidyl ethers with aglycol or an urethane. Examples of the glycol-modified, glycidyl etherresins include the compounds having the following general formula:##STR1## wherein R stands for --CH₂ CH₂ --OCH₂ CH₂ --_(n), --CH₂ CH₂ CH₂--OCH₂ CH₂ CH₂ --_(n) or --CH₂ CH₂ CH₂ CH₂ --OCH₂ CH₂ CH₂ CH₂ --_(n)where n is a positive interger, and Ph stands for p-phenylene.

Examples of the urethane-modified, glycidyl ether resins include thecompounds having the following general formulas: ##STR2## wherein Rstands for an alkykene, o-, m- or p-phenylene, o-, m- or p-phthaloyl,--Ph--CH₂ --Ph--, --Ph--C(CH₃)₂ --Ph--, --Ph--CHCH₃ --Ph-- or --CH₂ CH₂O--_(m) where Ph is p-phenylene and m is a positive integer, R' standsfor p-phenylene, alkylene or --Ph--CH₂ --Ph--_(m) where Ph and m are asdefined above, R" stands for hydrogen or methyl, X stands for--O--CO--NH --R'--NH--CO--O-- and n is a positive integer.

The glycidyl ether of bisphenol is preferably used in an amount of95-50% by weight, while the flexible epoxy resin is used in an amount of5-50% by weight.

The curing agent to be used in the present invention is preferably alatent curing agent which does not react with the mixed epoxy resin atroom temperature but can react therewith at a temperature of 60° C. ormore, preferably 100° C. or more. As such a curing agent, there may bepreferably used a nitrogen-containing, latent curing agent, such asdicyanodiamide, a guanamine, e.g. acetoguanamine and benzoguanamine, ahydrazide, e.g. adipodihydrazide, stearodihydrazide,isophthalodihydrazide and sebacohydrazide, or a triazine compound, e.g.2,4-dihydrazide-6-methylamino-S-triazine. Especially preferred is theuse of dicyanodiamide. The latent curing agent is preferably used in anamount of 0.03-2.0 moles per 1 equivalent of the epoxy group of themixed epoxy resins.

It is preferred that a curing accelerator be used in conjunction withthe above curing agent. Such a promoter may be, for example,3-substituted-1,1-dimethylureas, imidazole derivatives and solidsolution of 1,8-diaza-bicyclo(5,4,0)undecene-7 and phenol novolak.Examples of suitable urea compounds are3-(3,4-dichlorophenyl)-1,1-dimethylurea,3-(p-chlorophenyl)-1,1-dimethylurea, 3-phenyl-1,1-dimethylurea,N,N'-(4-methyl-1,3-phenylene)-bis(N,N'-dimethylurea) and5-(N,N'-dimethylureido)-1-(N",N"-dimethylureidomethyl)-1,3,3-trimethylcyclohexane.The curing accelerator is is suitably used in an amount of 1-30 partsper 100 parts of the mixed epoxy resin.

An inorganic filler is incorporated into the composition of the presentinvention. Illustrative of the inorganic fillers are silica, alumina,titania, calcium carbonate, talc, clay, calcium silicate, mica, glassfibers, glass powder, glass flakes and whiskers of various kinds. Theamount of the inorganic filler is 1-400 parts by weight, preferably10-300 parts by weight per 100 parts by weight of the mixed epoxyresins. The inorganic filler should have an average particle size of0.1-5 μm. Too large a particle size is disadvantageous because thepenetrability of the resulting composition becomes poor.

In the present invention a thixotropic agent, preferably having anaverage particle size of 100 nm or less is preferably used. Examples ofsuch a thixotropic agent include super-fine silica and alumina, aluminumhydroxide, fibrous magnesium oxysulfate, powdery asbesto, fibroussilica, fibrous potassium titanate, scale-like mica, and amontmorillonite-organic salt composite referred to as bentonite. Thethixotropic agent is used in an amount of 0.1-30 parts by weight,preferably 0.5-15 parts by weight per 100 parts by weight of the epoxyresin.

An organic solvent is incorporated into the composition of the presentinvention in such an amount as to maintain the viscosity thereof in therange of 50,10,000 cP at 25° C. The organic solvent serves not merely asa diluent but also as a solvent for the curing agent. It is a commonpractice to incorporate a reactive diluent such as 1,6-hexanedioldiglycidylether into epoxy resin compositions so as to lower theviscosity thereof. It has been found, however, that such a reactivediluent causes precipitation of the curing agent so that the compositionfails to show suitable penetrability and homogeneity. As a consequence,a cured body obtained from such a composition becomes poor in bondingstrength and heat resistance. It is also important that the organicsolvent be evaporated and removed from the cured mass during its curingstage, since otherwise tight bonding between articles to be bondedcannot be accomplished.

The organic solvent preferably has a boiling point of 40°-220° C., morepreferably 60°-160° C. Examples of such organic solvents includemethanol, N,N-dimethylformamide, 2-ethoxyethanol, dimethyl sulfoxide,ethylene glycol monomethyl ether, ethylene glycol monoethyl ether andethylene glycol dialkyl ethers. Of these, the use of methanol,N,N-dimethylformamide, ethylene glycol monomethyl ether or ethyleneglycol monoethyl ether is especially preferred.

The organic solvent is used in an amount so that the composition has aviscosity (25° C.) of 50-10,000 cP, preferably 500-5,000 cP. The amountof the organic solvent is generally 2-50 parts, preferably 5-30 parts byweight per 100 parts by weight of the mixed epoxy resin.

The composition according to the present invention may further contain,as desired, a reactive diluent, a flame retarder, a coupling agent, aleveling agent, a lubricating agent, an ooze-preventing agent, asedimentation-preventing agent, a dispersing agent, anadhesion-imparting agent, a wetting agent or a pigment. Examples of thereactive diluent include a polyoxyalkylene glycol glycidyl ether,phenoxyether monoepoxide, 1,6-hexanediol diglycidyl ether, phenylglycidyl ether and 2-ethylhexyl glycidyl ether.

Because of the incorporation of an organic solvent, the epoxy resincomposition of the present invention has excellent penetrability and isespecially suited for use as an adhesive for bonding a ferrite magnet toa motor yoke.

In bonding a ferrite magnet to a motor yoke with the composition of thepresent invention, the ferrite magnet is first attached at a desiredposition to the motor yoke by utilizing its magnetic force so that a gapof 0.02-1 mm is defined therebetween. Then, a predetermined quantity ofthe composition is applied by, for example, dropping from a dispenser,onto an upper portion of the gap between the motor yoke and the ferritemagnet. All that is subsequently needed is to place the resultingassembly in an oven. Because of the excellent penetrability of thecomposition of the present invention, it swiftly flows down into the gapbetween the motor yoke and the ferrite magnet. The composition is thencured with the simultaneous vaporization of the organic solvent. Theheating temperature in the oven is generally 100°-220° C., preferably150°-180° C. and the heating time is 5-120 minutes, preferably 15-60minutes. In this manner, the ferrite magnet can be tightly bonded to themotor yoke by a simple operation.

The cured mass obtained from the epoxy resin composition according tothe present invention contains substantially no organic solvent and isexcellent in adhesion and strength. Further, the use of the mixed epoxyresin can give a cured resin which is excellent in bending strength andthermal expansion/shrinkage properties and does not cause cracking.

The following examples will further illustrate the present invention,wherein "part" is by weight. The test methods employed in the examplesare as follows:

(1) Gellation time: In accordance with JIS C 2105, a test sample (0.4cc) is placed on a hot plate at 150° C. The period of time required forthe sample to gel is measured.

(2) Under shear adhesive strength: In accordance with JIS K 6850, a testsample is applied to one longitudinal margin (width of 10 mm) of a steelplate having a length of 100 mm, a width of 25 mm and a thickness of 1.6mm, on which another steel plate having the same size is superimposed.After heating at 180° C. for 30 minutes, the bonded plates are measuredfor their adhesive strength under shear.

(3) Glass transition point: A test sample is cured at 120° C. for 1 hourand thereafter at 180° C. for 30 minutes to obtain a cured resin platewith a thickness of about 3 mm. The plate was cut to form a rectangularrod of about 3×4×20 mm size. The rod is subjected to thermal mechanicalanalysis (TMA) with a heating rate of 5° C./minute. The point ofinflection in the resulting thermal expansion curve represents the glasstransition point of the sample.

EXAMPLE 1

A liquid epoxy resin composition containing 70 parts of a glycidyl etherof bisphenol A (Epikote 828, manufactured by Yuka-Shell Epoxy Inc.), 30parts of a flexible epoxy resin (urethane-modified epoxy resin EPU-6,manufactured by Asahi Denka Inc.), 2 parts of a curing accelerator(3-(p-chlorophenyl)-1,1-dimethylurea), 0.25 part of colloidal silica, 20parts of titanium oxide, 0.5 part of 2-methylimidazole-triazine and 28parts of a solution obtained by dissolving 8 parts of dicyanodiamide in20 parts of N,N-dimethylformamide (DMF) was prepared. This compositionhad a viscosity (25° C.) of about 1,200 cP, a gellation time of 200seconds, an under shear adhesive strength (after curing) of 180 kg/cm²and a glass transition point (after curing) of 120° C.2-Methylimidazoletriazine is a compound having the formula: ##STR3##

A given amount (about 0.5 g) of the above composition was placed on anupper portion of a gap of about 0.1 mm between a motor yoke and aferrite magnet bonded to the yoke by the magnetic force thereof. Thenthe assembly was placed and heated in an oven at 180° C. for 30 minutesfor curing. As a result, it was confirmed that the composition floweddown into the gap and cured. The ferrite magnet was found to be tightlybonded to the motor yoke with the cured resin. The cured resin was foundto be substantially free of N,N-dimethylformamide.

EXAMPLE 2

Example 1 was repeated in the same manner as described except that thecuring accelerator was used in an amount of 2.5 parts and that the2-imidazole-triazine was not used. The composition had a viscosity (25°C.) of about 1,200 cP, a gellation time of 210 seconds, an under shearadhesive strength (after curing) of 185 kg/cm² and a glass transitionpoint (after curing) of 120° C. With this composition, a ferrite magnetwas bonded to a motor yoke in a manner similar to that in Example 1.Tight bonding was obtained.

COMPARATIVE EXAMPLE 1

A liquid epoxy resin composition containing 70 parts of a glycidyl etherof bisphenol A (Epikote 828, manufactured by Yuka-Shell Epoxy Inc.), 30parts of a flexible epoxy resin (urethane-modified epoxy resin EPU-6,manufactured by Asahi Denka Inc.), 2.6 parts of a curing accelerator(3-(p-chlorophenyl)-1,1-dimethylurea), 0.25 part of colloidal silica, 20parts of titanium oxide, 10 parts of dicyanodiamide and 30 parts of areactive diluent (phenyl glycidyl ether) was prepared. This compositionhad a viscosity (25° C.) of about 1,300 cP, a gellation time of 280seconds, an under shear adhesive strength (after curing) of 100 kg/cm²and a glass transition point (after curing) of 85° C. The curing agentwas found to precipitate when the composition was allowed to stand at25° C. for 4 hours.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all the changes which come within the meaning and rangeof equivalency of the claims are therefore intended to be embracedtherein.

What is claimed is:
 1. A penetrable, epoxy resin compositioncomprising:a liquid, epoxy resin mixture containing (1) a glycidyl etherof bisphenol having an epoxy equivalent of 158-270 and (2) a glycidylether of a bisphenol modified with a glycol or an urethane; a curingagent capable of reacting with said epoxy resin mixture when heated to acuring temperature; an inert organic solvent which does not react withsaid epoxy resin mixture, which is capable of dissolving said curingagent and which has a boiling point lower than said curing temperature;and an inorganic filler having an average particle size of 0.1-5 μm,said composition having a viscosity of 50-10,000 cP at 25° C.
 2. Acomposition as claimed in claim 1, wherein said epoxy resin mixture iscomposed of 50-95 parts by weight of glycidyl ether of bisphenol A,bisphenol F or bisphenol AD and 5-50 parts by weight of anurethane-modified, glycidyl ether of bisphenol A, bisphenol F orbisphenol AD.
 3. A composition as claimed in claim 1, wherein saidorganic solvent has a boiling point of 40°-220° C.
 4. A composition asclaimed in claim 1, wherein said organic solvent is at least one memberselected from the group consisting of methanol, N,N-dimethylformamide,2-ethoxyethanol, dimethyl sulfoxide, ethylene glycol monomethyl ether,ethylene glycol monoethyl ether and ethylene glycol dialkyl ethers.
 5. Acomposition as claimed in claim 1, wherein said curing agent is at leastone member selected from dicyanodiamide, guanamines, hydrazides andtriazines.
 6. A composition as claimed in claim 1, wherein said curingagent is dicyanodiamide and said organic solvent is selected from thegroup consisting of methanol, N,N-dimethylformaide, ethylene glycolmonomethyl ether and ethylene glycol monoethyl ether.
 7. A compositionas claimed in claim 1, further comprising a thixotropy impartingsubstance.
 8. A composition as claimed in claim 1, further comprising acuring accelerator selected from the group consisting of3-substituted-1,1-dimethylureas, imidazole derivatives and solidsolution of 1,8-diazabicyclo(5,4,0) undecene-7 and a phenol novolak. 9.A composition in accordance with claim 1 having a viscosity of 500-5,000cP.